1. Field of the Invention
The present invention relates to a drive system for a vehicle, more particularly, to a drive system capable of transmitting driving force of a longitudinally mounted engine through a continuously variable transmission to drive wheels of the vehicle.
2. Prior Art
A belt driven continuously variable transmission has a primary pulley mounted on a primary shaft, a secondary pulley mounted on a secondary shaft provided in parallel with the primary shaft and a belt looped over the primary and secondary pulleys. Generally, the pulley diameter of the primary and secondary pulleys is determined based on miscellaneous design requirements such as pulley strength, belt strength, speed ratio and others. As a result, the pulleys need some amount of diameter and therefore a large distance is needed between the primary and secondary shafts. In case of a transversely mounted engine, that is, an engine whose crank shaft is arranged in the widthwise direction of the vehicle, such distance is not so big problem because the transversely mounted engine provides a relatively large longitudinal space in an engine room.
On the other hand, in a longitudinally mounted engine, an engine whose crank shaft is arranged in the longitudinal direction of the vehicle, since the primary shaft of the continuously variable transmission is connected with the crank shaft through a starting apparatus such as torque converter, electromagnetic clutch and the like, the secondary shaft must be arranged under the primary shaft. This arrangement requires a large vertical size to the transmission and also increases agitation loss of lubrication oil.
Further, in case of a vehicle such as front wheel drive vehicle or four wheel drive vehicle, a front differential must be incorporated in the engine room. In this case, a problem is that the total vertical length of the continuously variable transmission including the front differential extends further downwardly. In order to reduce the vertical length of the transmission, it is considered that the differential is arranged in an offsetting manner from the center of the vehicle to a left or right side. The problem of this arrangement is an unbalance in weight due to the left and right drive axles with unequal length.
In general, in case where an engine is longitudinally mounted, the longitudinal length of the engine room tends to become large. It is desirable to reduce the longitudinal size of the drive system in order to secure a large space of the passenger compartment. Particularly, it is desirable to design so as not to make a protrusion of a toe board into the passenger compartment.
Japanese Patent Applications Laid-open No. Toku-Kai-Hei 9-267652 and No. Toku-Kai-Hei 9-277842 disclose drive systems having a belt driven continuously variable transmission combined with a longitudinally mounted engine.